Browse Prior Art Database

Memory Sharing for Personal Computers

IP.com Disclosure Number: IPCOM000104820D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 77K

Publishing Venue

IBM

Related People

Keener, DS: AUTHOR [+3]

Abstract

Described is a circuit implementation whereby a single static random-access memory (RAM) module is used to share functions in a personal computer (PC) system. The circuit enables a single static RAM to be used for both non-volatile RAM (NVRAM) and small computer systems interface (SCSI) subsystem functions.

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Memory Sharing for Personal Computers

      Described is a circuit implementation whereby a single static
random-access memory (RAM) module is used to share functions in a
personal computer (PC) system.  The circuit enables a single static
RAM to be used for both non-volatile RAM (NVRAM) and small computer
systems interface (SCSI) subsystem functions.

      In prior art, micro-controller subsystem functions, such as
NVRAM and SCSI, utilized self-contained stand-alone logic and
required an individual RAM.  The concept described herein provides a
means whereby both NVRAM and SCSI memory functions are shared in such
a way as to utilize a single static RAM module, thereby saving
valuable space on a circuit board.

      The concept of using the single static RAM is accomplished by
sensing when one function is not using the RAM and then allowing the
other function to access the RAM during this time.  Typically, NVRAM
functions require less frequent RAM accesses than SCSi accesses.
Assuming that the micro-controller does not have a '"wait" state
capability, the objective is to determine when the micro-controller
is not using the RAM and then allow the NVRAM to access at that time.

      Fig. 1.  shows the block diagram of the RAM sharing circuitry.
Multiplexers (MUX), consisting of address MUX 10, data MUX 11 and
write MUX 12, are used to switch RAM 13 connections from
micro-controller 14 to NVRAM when NVRAM cycle is being performed.
The PSEN line from the P...